In the past, it has been proposed to provide mask parts around intake openings opened and closed by intake valves (for example, Japanese Patent Publication No. 2010-185457 A). The mask parts are provided with wall surfaces formed so as to extend along the outer edges of the intake openings toward the inside of the combustion chamber, at the opposite sides to the exhaust opening sides (below, referred to as the “opposite exhaust opening sides”).
The wall surfaces of such mask parts function as flow resistances against part of the intake gas taken in from the intake ports into the combustion chamber, when the intake valves are lifted. The intake gas passing through regions positioned at the opposite exhaust opening sides of the intake openings is thereby prohibited or inhibited from flowing into the combustion chamber. As a result, a reverse tumble flow is kept from being generated in the combustion chamber and a strong normal tumble flow is formed in the combustion chamber.